Such a color fringe is attributed to chromatic aberration, a known image defect in optical systems, which is associated with the dependence of the refractive index of the optical materials on the wavelength of the light passing through. In imaging optical systems such as microscopes, telescopes and cameras, achromatic elements or apochromatic elements have long been used to suppress chromatic aberration. These elements are lens systems in which the materials of several lenses mounted closely one behind the other complement each other in such a manner that the lens system has exactly corresponding focal lengths at two or three wavelengths of the visible spectrum.
Little attention has been paid so far to chromatic aberration in the design of headlights, since the conventionally used filament light sources have a continuously decreasing brightness at their edges and chromatic aberration is hardly visible at the edges of the light cone projected with the aid thereof. However, a chromatic dispersion becomes visible in this case at the edge of a screen that blocks some of the light flux.
A vehicle headlight in which an achromatic element is used to suppress a color fringe at a screen edge is known from DE 10 2010 046 626 A1. In the achromatic element, a projection lens, a diffuser lens and an interstice filled with a transparent medium are connected to form a structural unit. The interstice simplifies the manufacture of the lenses of the achromatic element, since the lens surfaces that face each other do not have to have exactly the same curvatures. On the other hand, the assembly thereof is made more complicated, since the lenses must be supported independently of each other and the interstice between them must be sealed.
Accordingly, there is a need to provide a vehicle headlight with correction of the chromatic aberration that is cost-effective and simple to manufacture.